Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
van hanh » van thanh, ban hanh, van anh
thuc van » thuc vat, thuc dan, thuc va
nam thuc » nam thuoc, am thuc, nam thu
hieu van » thien van, lieu va, hieu ve
thu sach » tu sach, thuat sach, thuoc sach
cua viet » ca viet, hoa viet, cua vat
nang ma » tang ma, sang ma, nang cao
lo nang » ho nang, ly nang, loai nang
hieu va » lieu va, hieu qua
ma hoi » mai hoi, xa hoi, ma hoa
vi cua » vai cua, di cua

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: ((toc sach) or (thu sach)) lo nang ma hoi. ((hieu van) or (hieu va)) nam thuc van hanh vi cua viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (thu sach)) lo nang ma hoi. ((hieu van) OR (hieu va)) nam thuc van hanh vi cua viet.
• Adding a wildcard symbol may retrieve word variants: ((toc sach) or (thu sach)) lo nang ma hoi. ((hieu van) or (hieu va)) nam thuc van hanh vi cua viet*.